TL neuro

July 29, 2015

Modeling the preference for peers that you get high with

Filed under: Animal Models, Behavior, Cocaine, Neuroscience — mtaffe @ 1:02 pm

A new paper from Mark Smith and colleagues addresses whether drug exposure can differentially condition a preference for certain peers in a rat model.

Smith MA, Strickland JC, Bills SE, Lacy RT. The effects of a shared history of drug exposure on social choice. Behav Pharmacol. 2015 Apr 28. [Epub ahead of print]

The study focused on “choice” rat groups, one of which (N=16) was to receive cocaine injections and one of which (N=16) was to receive saline injections. The choice rats were then destined to have social interactions with a social peer rat that had received cocaine or a social rat that had received saline.

Smith15-RatPrefThe social choice apparatus is depicted in this figure from the paper. The choice rat is permitted to roam about the apparatus and choose proximity to one of two partner rats. A pre-conditioning test established the amount of time a given choice rat spent in proximity to each of the saline- or cocaine-treated partner rats.

The choice rats then underwent a total of 10 conditioning sessions in normal home cages. For these sessions, the choice rats would receive their cocaine or saline injections and then interact with a single partner rat for 30 min. On five of those sessions the partner rat was as cocaine treated animal and on the other five the partner was saline treated.

The critical post-conditioning preference test was then conducted.

A change in preference was expressed as the amount of time spent on the side of the apparatus containing each partner rat divided by the time spent with that partner during the pre-conditioning test. Two analyses were conducted, one just scoring time in each half of the apparatus and a second analysis scoring time spent in ~the front half of each side, i.e., in closer proximity to the partner. This made no difference in the results, including the fact that there was no change in the amount of time spent in this “neutral” or non-social zone after conditioning.

The takeaway message was that there was a significant increase in the amount of time spent with the similarly-treated partner when all choice rats were considered. However when the group analysis was conducted, only the cocaine-treated choice rats exhibited increased preference for the cocaine-treated partner. Saline-treated choice rats had no partner preference.

The takeaway message is that cocaine-treated rats prefer to hang out with other cocaine-treated rats. It wasn’t a general social-conditioning effect, since there was no differential effect on time spent in the non-social part of the apparatus.

There is one major caveat. The size of the effect was about an 8% increase in the time cocaine-treated choice rats spent with the cocaine-treated partner during the choice test. This amounted to about 49 seconds.

This is a limited initial finding but it obviously has promise for investigating social factors that enhance or diminish drug preferences, drug reward and the power of drug-related cues to shape behavior.

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